Changing the shape and color of keratinous fibers, particularly hair, is an important area of modern cosmetics. In this way, the appearance of hair can be changed to reflect both current fashion trends and the personal desires of an individual. Coloring, particularly covering grey hair, is desired by many people.
Various coloring systems for changing the color of hair are known the person skilled in the art, depending on the requirement the coloring must meet. For permanent, intense colors with good fastness properties and good grey coverage, as a rule oxidizing dyes are used. Such dyes typically contain oxidation dye precursors, “also called primary and secondary intermediates”, which combine to form the actual dyes under the effects of oxidizing compositions such as hydrogen peroxide. Oxidation dyes are characterized by excellent, long-lasting coloring, but are also associated with a certain quantity of hair damage.
Hair color can be changed temporarily through the use of directly absorbed dyes. In these cases, already fully prepared colorants diffuse from the dye into the hair fibers. In order to improve dye diffusion, it is common to add one or more organic solvents to the colorant recipe, such solvents being selected from lower alkylene carbonates, e.g., propylene carbonate, aromatic alcohols, particularly benzyl alcohol, phenoxyethanol or benzyloxyethanol, and N-alkylpyrrolidones, particularly N-methylpyrrolidone.
Compared to oxidation hair dyeing, the coloring results obtained with directly absorbed dyes do not last as long and wash out sooner. The grey coverage achievable with directly absorbed dyes generally also needs improvement. However, one advantage is that less damage is caused to the hair by directly absorbed dyes. Consequently, the use of directly absorbed dyes is the dyeing method of choice in order to minimize hair damage.
Direct-dyeing colorants are often formulated and marketed as shampoo preparations. Many attempts have also been made to develop other packaging forms. For example, it has been suggested to apply thinner colorant in the form of a foam. Particularly in the case of foam application, the use of aerosol foams is widespread.
A problem with foam application is that of stabilizing the foams. The consistency of foams is described as ideal when a firm, stable foam is formed upon dispensing which leaves a silky feeling and only breaks slowly on the hair. However, it has often been found that the foams delivered are unstable and quickly collapse back into themselves, so that a low-viscosity, dripping solution remains. On the other hand, it is also essential that the foam still wets the hair thoroughly to ensure good dye coverage. The stability of the foam is particularly adversely affected by the presence of large quantities of organic solvents.
Hair dyes in foam form for direct hair coloring containing from about 5 to about 65 wt % organic solvents including low alkylene carbonates and aromatic alcohols as particularly suitable solvents have been disclosed previously in patent document JP61210023A. Foam hair dyes for direct hair coloring which disclose aromatic alcohols and N-alkyl pyrrolidones as particularly suitable solvents are known from German patent DE19653496A1.
However, the foaming properties of the foams produced thereby were still not entirely satisfactory, particularly with respect to the breaking of the foam when it is spread on the hair, in order to ensure optimal distribution of the coloring composition and optimal impregnation of the dye by the hair.